Question The buggy result of a AlphaTest (with shadow) Shader

Hey there,

I downloaded model and textures from DOTA2 and wrote a shader for it. Everything goes right except for the shadow.

I learned that if I want to add shadow in an AlphaTest shader, I will need to add a "_Cutoff " and a "_Color" property, and set the FallBack to "Legacy Shaders/Transparent/Cutout/VertexLit".

I did that. However something wired just happend. Actually I don't know how to describe that properly...

Here are some clues:
1. The shadow will disappear when I push down the mouse button (like drag and rotate)
2. The shadow reappears after I release the button for a while. And I can see some noise if I take a closer look.
3. I can see the model (just a contour) behind it if I hold down the mouse button, just like being some what transparent.
4. The model become opaque again when I release the button.
5. If the "_Cutoff " property is commented, ALL of the above will GONE.

I'm just going to go mad about this stuff... I have an another shader from internet that goes well with AlphaTest & shadow & _Cutoff, but I just don't know what made all these happened...

Help, and thanks. QWQ

 

I upload a video on YouTube.
If someone curious about what happened on earth, go have a look...